Synchronization among Pedestrians in Footbridges due to Crowd Density

Abstract

Crowding is a critical condition for footbridges that are prone to vibration problems from pedestrian loads. Synchronization of pedestrian movements has been identified as the cause of the excessive lateral vibration in some footbridges. Two conditions have been named as the cause of synchronization: increase in crowd density and pedestrian-structure interaction. The former would be related to the onset of the phenomenon; the latter takes place after structural vibration reaches a certain level. This paper focuses on the former condition. A test program to investigate whether this condition occurs was carried out for a range of pedestrian densities, complementing data previously published on this subject. The head movement of pedestrians walking both in groups and in a flow was recorded by a video camera, and the examination of the video indicated no synchronization from densification. However, it was observed that the lateral sway of the pedestrians’ bodies increased with the increase of density. By using an existing model of an inverted pendulum to estimate lateral forces applied by a pedestrian and using the collected data as input to the model, a steady increase of lateral force from the rise in density was observed: it reached a 104% increase for a density of 1.8 pedestrians/m